The present invention relates to a flexible submarine piper intended for transporting fluids in deep water. These fluids are notably gases or liquids, preferably hydrocarbons.
Flexible pipes for transporting hydrocarbons generally include from the outside to the inside of the piper:                an external polymeric sheath for protecting the whole of the pipe and notably for preventing seawater from penetrating its thickness,        tensile armouring webs,        a pressure vault,        a sealed internal polymeric sheath, and        optionally a metal carcass (FIG. 1).        
If the piper comprises a metal carcass, it is said to be with a rough passage (rough bore). If the pipe is without any metal carcass, it is said to be with a smooth passage. Generally for transporting hydrocarbons, a pipe including a carcass is preferred, while a pipe without any carcass will be suitable for transporting water and/or pressurized steam.
The metal carcass and the pressure vault consist of longitudinal elements wound with a short pitch, and they give the pipe its resistance to radial forces while the tensile armouring webs consist of metal wires wound with long pitches in order to absorb the axial forces.
The nature, the number, the dimensioning and the organization of the layers making up the flexible pipes are essentially related to their conditions of use and installation. The pipes may comprise additional layers to the aforementioned ones.
In the present application, the notion of a winding with a short pitch designates any helical winding with a helix angle close to 90°, typically comprised between 75° and 90°. The notion of a winding with a long pitch, as for it, covers helix angles of less than 55°, typically comprised between 25° and 55° for armouring webs.
These flexible pipes are notably suitable for the transport of fluids, notably of hydrocarbons on the seabed and this at great depths. More specifically, they are said to be of the unbonded type and they are thus described in normative documents published by the American Petroleum Institute (API), API 17J and API RP 17B.
Flexile pipes may be used at great depth, typically down to 2,500 meters deep. They allow transport of fluids, notably of hydrocarbons, having a temperature typically attaining 130° C. and which may even exceed 150° C. and an internal pressure which may attain 1 000 bars or even 1 500 bars.
The constitutive material of the internal sealed polymeric sheath should be chemically stable and capable of mechanically withstanding the transported fluid and its characteristics (composition, temperature and pressure). This material should combine characteristics of ductility, of strength over time (generally, the pipe should have a lifetime of at least 20 years), of mechanical strength, of resistance to heat and pressure. The material should notably be chemically inert towards the chemical compounds making up the transported fluid.
Pipes comprising an internal sealed polymeric sheath based on a polymer, notably on polyamide, on grafted polyethylene (Crossflex®) or on polyvinylidene fluoride, may notably be used. However, the thermo-mechanical properties of the polymers under the aforementioned conditions of use (high temperature and pressure, high acidity and presence of water) may be clearly reduced. In particular, polyamides may be degraded by hydrolysis. Further, it is difficult to use polyethylenes at temperatures above 65° C. Thus, many studies have been reported on attempting to improve these properties, in particular for improving their creep and tensile or compressive strengths and allowing their use under the aforementioned conditions of temperatures and pressure.
International application WO 2008/113362 describes a flexible pipe comprising a layer comprising a polymeric resin comprising a cationic clay of the silicate type bonded in a non-covalent way to the polymer, this clay being described as giving the possibility of increasing the resistance to corrosion and improving the mechanical strength of said layer.
However, the preparation of the layer in which the cationic clay, in the form of sheets, is homogeneously distributed, is generally not very easy. Now, the homogeneity of the layer is very substantial, since more the sheets are independent of each other and homogeneously distributed, the larger is the contact surface area between the polymer and the sheet, and the more the impact of the clay on the improvement of the properties is perceivable.
Thus, WO 2008/113362 describes a method for preparing the layer which is different from a conventional method for preparing a polymeric resin, in that it requires:                sufficient shearing for obtaining adequate homogeneity,        that compounding be carried out at lower temperatures than those customarily used,        an exfoliation and/or intercalation step (intercalation of a polymer or of a quaternary amine between the sheets in order to space them apart) be added.        
One of the goals of the present invention is to provide a flexible submarine pipe comprising a layer based on polymer having improved thermo-mechanical properties allowing its use for transporting fluids, such as hydrocarbons, notably at high pressure and high temperature and which may be prepared by a conventional method for preparing a polymeric resin, in particular which does not require any exfoliation step.